1. Technical Field
The present invention relates to integrated circuit processing and more particularly to a device and method which employ angle ion implantation to selectively alter an etch rate to re-shape sidewall image transfer patterns.
2. Description of the Related Art
Sidewall Image Transfer (SIT) has been widely used, for example, to form narrow fins for FinFETs (fin field effect transistors). The conventional SIT process requires an additional mask level to remove the undesirable or unwanted parts/sides of the SIT structure. For example, after fin sidewall imaging transfer, the additional mask is used to cut the ends of the fins. Using an extra mask level has drawbacks such as increased mask cost, process cost and process complexity.
Current integration uses SIT to double pattern densities and requires an extra resist mask step to remove the undesirable or un-wanted parts/sides formed by the SIT integration process. Using an extra resist mask step, a few ways exist to etch off the undesirable or un-wanted parts/sides. All of these ways require very high etching selectivity to remove the undesirable or un-wanted parts/sides over a lower layer, to form a final desirable or wanted pattern.
A typical process flow creates a poly silicon mandrel, forms spacers wrapping around the mandrel and uses the spacers as masks to open a lower oxide layer. Remaining spacers are etched off to reduce topography, and a resist mask is processed to expose undesirable parts of oxide masks. Using resist masks, the undesirable parts of the oxide masks are removed. The resist masks are stripped. Then, the oxide masks are employed to etch silicon of a silicon-on-insulator structure to form more densely pitched fin lines.